The invention relates to an on-line attenuation device for a monomode fibre. It also relates to a method of manufacturing such a device.
1. Field of the Invention
The field of the invention is that of optical telecommunications and more particularly that of distribution networks.
Distribution networks relate to short-distance links and require significant resources in terms of cost both with regard to the infrastructure and the components. It is in this context that the invention is situated.
It should be stated that there may be a need to use optical attenuators notably in order to obtain an equalisation of the powers of the signal of several communication channels. It is also possible to use such attenuators in order to produce optical interferometers. There may also be a need to use optical attenuators in the laboratory in order to simulate optical transmission lines.
2. Discussion of the Related Art
The fixed on-line attenuators on optical fibres which are used most often are those which use the following techniques:                transverse offset of two fibres during their welding. This technique is described in the document WO 931 437;        the use of the curvature of the fibre in order to attenuate the signal. Such a technique is described in the document U.S. Pat. No. 5,581,649;        thinning of the fibre;        the use of a section of attenuating doped fibre between two monomode fibres. This technique is described in the document U.S. Pat. No. 5,633,974;        a section of pure undoped silica without a guide, welded between two monomode fibres. This technique is described in the document U.S. Pat. No. 5,095,519;        a section of fibre with an index gradient held by a ferrule between two optical fibres. This technique is described in the document JP 62 119503 A.        
The technology of attenuators which uses the principle of offset or thinning is not compatible with mass production methods.
The attenuators functioning on the principle of the use of a radius of curvature or a doped section require fairly complex implementation. And the technique of attenuators with a section of undoped fibre does not make it possible to have very broad manufacturing tolerances.
In addition, apart from the complexity introduced with regard to the connection of the fibres by the ferrule, the attenuator with a section of fibre with an index gradient is not suited to a collective production and does not make it possible to have very broad manufacturing tolerances.